The present invention relates to a joining structure for a semiconductor device such as an LSI mounted on a multilayered wiring board, a thick-film multilayered board, a semiconductor package, an insulating board using a glass-ceramic, or the like and, more particularly, to the structure of an element joining pad formed on a semiconductor device mounting board.
FIG. 3 shows a conventional joining pad of a metalized arrangement formed on a semiconductor device mounting board. A metalized layer on a mounting board is generally constituted by a thin film. The joining pad shown in FIG. 3 is constituted by a Cr sputtered film 8 selectively formed on a glass-ceramic board 7, and a Pd sputtered film 9 formed on the Cr sputtered film 8. When a thin-film metalized layer is used, although a residual stress which is generated by forming the metalized layer and acts on a board can be suppressed, the cost increases. FIG. 4 shows a case wherein an I/O pin is joined on a metalized arrangement. Referring to FIG. 4, an I/O pin 6 consisting of Kovar is joined by an Au--Sn brazing alloy 10 on the metalizing arrangement (FIG. 3) constituted by the Cr sputtered film 8 and the Pd sputtered film 9. In this manner, as a conventional brazing material used in a thin-film metalized layer, a material such as an Au--Sn-based alloy having a melting point of 300.degree. C. or less is often used. However, the Au--Sn alloy is expensive, and a temperature in the processes after the I/O pin 6 is joined is disadvantageously limited to the low temperature of the Au--Sn alloy due to its low melting point. In addition, when a brazing material having a melting point of 500.degree. C. or more, and particularly, 700.degree. C. or more is used, the brazing material and the metalizing material are diffused to each other, and a stress generated during a brazing operation disadvantageously peels a metalized film or breaks a board.
In order to solve this problem, in a conventional alumina or aluminum nitride board 11, as shown in FIG. 5, after a Ni plating layer 4 is formed on a thick-film tungsten metalized layer 12 formed on a board, an I/O pin 6 consisting of Kovar is joined to the Ni plating layer 4 with a Ag--Cu-based eutectic brazing material 5. However, in order to form the thick-film tungsten metalized layer 12, a process temperature must be set to be 1,500.degree. C. or more. For this reason, the same technique as described above cannot be applied to a glass-ceramic board which can be advantageously sintered at a low temperature.
A thick-film metalized layer is applied to a low-temperature sintered glass-ceramic board such that, as shown in FIG. 6, after the Ni plating layer 4 is formed on the thick-film Cu-metalized layer 13 formed on the glass-ceramic board 7, the I/O pin 6 consisting of Kovar is joined to the Ni plating layer 4 with the Ag--Cu-based material 5. However, in this case, the material of the thick-film Cu-metalized layer 13, the material of the Ni plating layer 4, and the Ag--Cu brazing material 5 are completely diffused to each other, so that a satisfactory joining strength cannot be obtained. In addition, when the portion of the thick-film Cu-metalized layer 13 consists of Ag or a Ag--Pd-based alloy, the diffusion can be suppressed. However, when the I/O pin 6 is joined to the Ni plating layer 4 with the Ag--Cu-based eutectic brazing material, the thick-film metalized layer 13 is disadvantageously peeled.
Applying a high-temperature brazing material to a glass-ceramic board is reported in Japanese Patent Laid-Open No. 2-88471. This technique is associated with a joining operation between the glass-ceramic board and an AlN board. According to the technique, the strength of a metalized layer is increased such that an intermediate layer consisting of glass and a metal is formed on a metalized portion consisting of glass-ceramic. However, when an I/O pin or the like is joined to the metalized layer, a satisfactory strength cannot be obtained.
As described above, a metalizing structure and a joining structure on a low-temperature sintered board, and particularly, a glass-ceramic board cannot join the board to a metal at a low cost and a high strength, and cannot obtain a joining member having a heat resistance of 500.degree. C. or more and constituted by a joining pad and a metal.